Possible Involvement of Nitric Oxide in Enhanced Liver Injury and Fibrogenesis during Cholestasis in Cytoglobin-deficient Mice

Molecular analysis of the human cytoglobin mRNA isoforms

Multiple functions have been proposed for the ubiquitously expressed vertebrate globin cytoglobin (Cygb), including nitric oxide (NO) metabolism, lipid peroxidation/signalling, superoxide dismutase activity, reactive oxygen/nitrogen species (RONS) scavenging, regulation of blood pressure, antifibrosis, and both tumour suppressor and oncogenic effects. Since alternative splicing can expand the biological roles of a gene, we investigated whether this mechanism contributes to the functional diversity of Cygb. By mining of cDNA data and molecular analysis, we identified five alternative mRNA isoforms for the human CYGB gene (V-1 to V-5). Comprehensive RNA-seq analyses of public datasets from human tissues and cells confirmed that the canonical CYGB V-1 isoform is the primary CYGB transcript in the majority of analysed datasets. Interestingly, we revealed that isoform V-3 represented the predominant CYGB variant in hepatoblastoma (HB) cell lines and in the majority of analysed normal and HB liver tissues. CYGB V-3 mRNA is transcribed from an alternate upstream promoter and hypothetically encodes a N-terminally truncated CYGB protein, which is not recognized by some antibodies used in published studies. Little to no transcriptional evidence was found for the other CYGB isoforms. Comparative transcriptomics and flow cytometry on CYGB+/+ and gene-edited CYGB-/- HepG2 HB cells did not unveil a knockout phenotype and, thus, a potential function for CYGB V-3. Our study reveals that the CYGB gene is transcriptionally more complex than previously described as it expresses alternative mRNA isoforms of unknown function. Additional experimental data are needed to clarify the biological meaning of those alternative CYGB transcripts.

Transcriptomics of a cytoglobin knockout mouse: Insights from hepatic stellate cells and brain

The vertebrate respiratory protein cytoglobin (Cygb) is thought to exert multiple cellular functions. Here we studied the phenotypic effects of a Cygb knockout (KO) in mouse on the transcriptome level. RNA sequencing (RNA-Seq) was performed for the first time on sites of major endogenous Cygb expression, i.e. quiescent and activated hepatic stellate cells (HSCs) and two brain regions, hippocampus and hypothalamus. The data recapitulated the up-regulation of Cygb during HSC activation and its expression in the brain. Differential gene expression analyses suggested a role of Cygb in the response to inflammation in HSCs and its involvement in retinoid metabolism, retinoid X receptor (RXR) activation-induced xenobiotics metabolism, and RXR activation-induced lipid metabolism and signaling in activated cells. Unexpectedly, only minor effects of the Cygb KO were detected in the transcriptional profiles in hippocampus and hypothalamus, precluding any enrichment analyses. Furthermore, the transcriptome data pointed at a previously undescribed potential of the Cygb- knockout allele to produce cis-acting effects, necessitating future verification studies.

The knockout of cytoglobin 1 in zebrafish (Danio rerio) alters lipid metabolism, iron homeostasis and oxidative stress response

Cytoglobin (Cygb) is an evolutionary ancient heme protein with yet unclear physiological function(s). Mammalian Cygb is ubiquitously expressed in all tissues and is proposed to be involved in reactive oxygen species (ROS) detoxification, nitric oxide (NO) metabolism and lipid-based signaling processes. Loss-of-function studies in mouse associate Cygb with apoptosis, inflammation, fibrosis, cardiovascular dysfunction or oncogenesis. In zebrafish (Danio rerio), two cygb genes exist, cytoglobin 1 (cygb1) and cytoglobin 2 (cygb2). Both have different coordination states and distinct expression sites within zebrafish tissues. The biological roles of the cygb paralogs are largely uncharacterized. We used a CRISPR/Cas9 genome editing approach and generated a knockout of the penta-coordinated cygb1 for in vivo analysis. Adult male cygb1 knockouts develop phenotypic abnormalities, including weight loss. To identify the molecular mechanisms underlying the occurrence of these phenotypes and differentiate between function and effect of the knockout we compared the transcriptomes of cygb1 knockout at different ages to age-matched wild-type zebrafish. We found that immune regulatory and cell cycle regulatory transcripts (e.g. tp53) were up-regulated in the cygb1 knockout liver. Additionally, the expression of transcripts involved in lipid metabolism and transport, the antioxidative defense and iron homeostasis was affected in the cygb1 knockout. Cygb1 may function as an anti-inflammatory and cytoprotective factor in zebrafish liver, and may be involved in lipid-, iron-, and ROS-dependent signaling.

Cellular stress in the pathogenesis of nonalcoholic steatohepatitis and liver fibrosis

The burden of chronic liver disease is rising substantially worldwide. Fibrosis, characterized by excessive deposition of extracellular matrix proteins, is the common pathway leading to cirrhosis, and limited treatment options are available. There is increasing evidence suggesting the role of cellular stress responses contributing to fibrogenesis. This Review provides an overview of studies that analyse the role of cellular stress in different cell types involved in fibrogenesis, including hepatocytes, hepatic stellate cells, liver sinusoidal endothelial cells and macrophages.

Essential Involvement of Neutrophil Elastase in Acute Acetaminophen Hepatotoxicity Using BALB/c Mice

Intense neutrophil infiltration into the liver is a characteristic of acetaminophen-induced acute liver injury. Neutrophil elastase is released by neutrophils during inflammation. To elucidate the involvement of neutrophil elastase in acetaminophen-induced liver injury, we investigated the efficacy of a potent and specific neutrophil elastase inhibitor, sivelestat, in mice with acetaminophen-induced acute liver injury. Intraperitoneal administration of 750 mg/kg of acetaminophen caused severe liver damage, such as elevated serum transaminase levels, centrilobular hepatic necrosis, and neutrophil infiltration, with approximately 50% mortality in BALB/c mice within 48 h of administration. However, in mice treated with sivelestat 30 min after the acetaminophen challenge, all mice survived, with reduced serum transaminase elevation and diminished hepatic necrosis. In addition, mice treated with sivelestat had reduced NOS-II expression and hepatic neutrophil infiltration after the acetaminophen challenge. Furthermore, treatment with sivelestat at 3 h after the acetaminophen challenge significantly improved survival. These findings indicate a new clinical application for sivelestat in the treatment of acetaminophen-induced liver failure through mechanisms involving the regulation of neutrophil migration and NO production.

Modulating Nitric Oxide Dioxygenase and Nitrite Reductase of Cytoglobin through Point Mutations

Cytoglobin is a hexacoordinate hemoglobin with physiological roles that are not clearly understood. Previously proposed physiological functions include nitric oxide regulation, oxygen sensing, or/and protection against oxidative stress under hypoxic/ischemic conditions. Like many globins, cytoglobin rapidly consumes nitric oxide under normoxic conditions. Under hypoxia, cytoglobin generates nitric oxide, which is strongly modulated by the oxidation state of the cysteines. This gives a plausible role for this biochemistry in controlling nitric oxide homeostasis. Mutations to control specific properties of hemoglobin and myoglobin, including nitric oxide binding/scavenging and the nitrite reductase activity of various globins, have been reported. We have mapped these key mutations onto cytoglobin, which represents the E7 distal ligand, B2/E9 disulfide, and B10 heme pocket residues, and examined the nitric oxide binding, nitric oxide dioxygenase activity, and nitrite reductase activity. The Leu46Trp mutation decreases the nitric oxide dioxygenase activity > 10,000-fold over wild type, an effect 1000 times greater than similar mutations with other globins. By understanding how particular mutations can affect specific reactivities, these mutations may be used to target specific cytoglobin activities in cell or animal models to help understand the precise role(s) of cytoglobin under physiological and pathophysiological conditions.

Capacity of extracellular globins to reduce liver fibrosis via scavenging reactive oxygen species and promoting MMP-1 secretion

Background & aims

Hepatic stellate cells (HSCs) are the primary cell type in liver fibrosis, a significant global health care burden. Cytoglobin (CYGB), a globin family member expressed in HSCs, inhibits HSC activation and reduces collagen production. We studied the antifibrotic properties of globin family members hemoglobin (HB), myoglobin (MB), and neuroglobin (NGB) in comparison with CYGB.

Approach & results

We characterized the biological activities of globins in cultured human HSCs (HHSteCs) and their effects on carbon tetrachloride (CCl₄)-induced cirrhosis in mice. All globins demonstrated greater antioxidant capacity than glutathione in cell-free systems. Cellular fractionation revealed endocytosis of extracellular MB, NGB, and CYGB, but not HB; endocytosed globins localized to intracellular membranous, cytoplasmic, and cytoskeletal fractions. MB, NGB, and CYGB, but not HB, scavenged reactive oxygen species generated spontaneously or stimulated by H₂O₂ or transforming growth factor β1 in HHSteCs and reduced collagen 1A1 production via suppressing COL1A1 promoter activity. Disulfide bond-mutant NGB displayed decreased heme and superoxide scavenging activity and reduced collagen inhibitory capacity. RNA sequencing of MB- and NGB-treated HHSteCs revealed downregulation of extracellular matrix–encoding and fibrosis-related genes and HSC deactivation markers. Upregulation of matrix metalloproteinase (MMP)-1 was observed following MB and NGB treatment, and MMP-1 knockdown partially reversed globin-mediated effects on secreted collagen. Importantly, administration of MB, NGB, and CYGB suppressed CCl₄-induced mouse liver fibrosis.

Conclusions

These findings revealed unexpected roles for MB and NGB in deactivating HSCs and inhibiting liver fibrosis development, suggesting that globin therapy may represent a new strategy for combating fibrotic liver disease.

Myoglobin, neuroglobin, and cytoglobin, but not hemoglobin:•

Internalize into human hepatic stellate cells via endocytosis pathway.

•

Scavenge intracellular reactive oxidative species.

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Suppress COL1A1 promoter activity and promote matrix metaloproteinase-1 secretion.

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Suppress carbon tetrachloride-induced mouse liver fibrosis.

Hexa Histidine-Tagged Recombinant Human Cytoglobin Deactivates Hepatic Stellate Cells and Inhibits Liver Fibrosis by Scavenging Reactive Oxygen Species

BACKGROUND AND AIMS

Antifibrotic therapy remains an unmet medical need in human chronic liver disease. We report the antifibrotic properties of cytoglobin (CYGB), a respiratory protein expressed in hepatic stellate cells (HSCs), the main cell type involved in liver fibrosis.

APPROACH AND RESULTS

Cygb-deficient mice that had bile duct ligation-induced liver cholestasis or choline-deficient amino acid-defined diet-induced steatohepatitis significantly exacerbated liver damage, fibrosis, and reactive oxygen species (ROS) formation. All of these manifestations were attenuated in Cygb-overexpressing mice. We produced hexa histidine-tagged recombinant human CYGB (His-CYGB), traced its biodistribution, and assessed its function in HSCs or in mice with advanced liver cirrhosis using thioacetamide (TAA) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). In cultured HSCs, extracellular His-CYGB was endocytosed and accumulated in endosomes through a clathrin-mediated pathway. His-CYGB significantly impeded ROS formation spontaneously or in the presence of ROS inducers in HSCs, thus leading to the attenuation of collagen type 1 alpha 1 production and α-smooth muscle actin expression. Replacement the iron center of the heme group with cobalt nullified the effect of His-CYGB. In addition, His-CYGB induced interferon-β secretion by HSCs that partly contributed to its antifibrotic function. Momelotinib incompletely reversed the effect of His-CYGB. Intravenously injected His-CYGB markedly suppressed liver inflammation, fibrosis, and oxidative cell damage in mice administered TAA or DDC mice without adverse effects. RNA-sequencing analysis revealed the down-regulation of inflammation- and fibrosis-related genes and the up-regulation of antioxidant genes in both cell culture and liver tissues. The injected His-CYGB predominantly localized to HSCs but not to macrophages, suggesting specific targeting effects. His-CYGB exhibited no toxicity in chimeric mice with humanized livers.

CONCLUSIONS

His-CYGB could have antifibrotic clinical applications for human chronic liver diseases.

Protective effect of apigenin magnesium complex on H2O2-induced oxidative stress and inflammatory responses in rat hepatic stellate cells

Context: Apigenin displays antioxidant and anti-inflammatory effects. However, effects of apigenin magnesium (AM) complex on these aspects remain unknown.Objective: This study investigated the effects of AM complex on oxidative stress and inflammatory responses in hydrogen peroxide (H₂O₂)-induced rat hepatic stellate cells (HSCs).Materials and methods: The antioxidant and anti-inflammatory effects of AM complex at concentrations of 0.625, 1.25, and 2.5 mg/mL were evaluated, comparing to HSCs treated by H₂O₂ alone. Cell viability, reactive oxygen species (ROS), the activity of superoxide dismutase (SOD), glutathione (GSH), malondialdehyde (MDA), nitric oxide (NO), interleukin 6 (IL-6), and nuclear factor-kappa B (NF-κB) levels were measured. Moreover, cell apoptosis, mRNA expression levels of transforming growth factor-β (TGF-β), NF-κB, and inducible nitric oxide synthase (iNOS) were assessed.Results: AM complex significantly inhibited oxidative stress and inflammatory response at concentrations of 0.625, 1.25, and 2.5 mg/mL (IC₅₀ = 1.679 mg/mL). AM complex elevated the survival rate of H₂O₂-treated HSCs and had no toxic effects on HSCs. AM complex also promoted SOD activity and GSH levels but suppressed ROS, MDA, and NO levels. Additionally, AM complex decreased IL-6 and NF-κB levels, gene expression of TGF-β, NF-κB, and iNOS, as well as induced apoptosis of HSCs.Discussion and conclusions: Data indicated that AM complex mitigated oxidative stress and inflammatory responses on H₂O₂-treated HSCs, suggesting that AM complex is a possible candidate for anti-hepatic diseases. Additional efforts, both in vivo and in humans, are required to assess of AM complex as a potential therapeutic drug in liver diseases.

TGF-β1-driven reduction of cytoglobin leads to oxidative DNA damage in stellate cells during non-alcoholic steatohepatitis

BACKGROUND & AIMS

Cytoglobin (CYGB) is a respiratory protein that acts as a scavenger of reactive oxygen species. The molecular role of CYGB in human hepatic stellate cell (HSC) activation and human liver disease remains uncharacterised. The aim of this study was to reveal the mechanism by which the TGF-β1/SMAD2 pathway regulates the human CYGB promoter and the pathophysiological function of CYGB in human non-alcoholic steatohepatitis (NASH).

METHODS

Immunohistochemical staining was performed using human NASH biopsy specimens. Molecular and biochemical analyses were performed by western blotting, quantitative PCR, and luciferase and immunoprecipitation assays. Hydroxyl radicals (^•OH) and oxidative DNA damage were measured using an ^•OH-detectable probe and 8-hydroxy-2'-deoxyguanosine (8-OHdG) ELISA.

RESULTS

In culture, TGF-β1-pretreated human HSCs exhibited lower CYGB levels - together with increased NADPH oxidase 4 (NOX4) expression - and were primed for H₂O₂-triggered ^•OH production and 8-OHdG generation; overexpression of human CYGB in human HSCs reversed these effects. Electron spin resonance demonstrated the direct ^•OH scavenging activity of recombinant human CYGB. Mechanistically, pSMAD2 reduced CYGB transcription by recruiting the M1 repressor isoform of SP3 to the human CYGB promoter at nucleotide positions ⁺2-⁺13 from the transcription start site. The same repression did not occur on the mouse Cygb promoter. TGF-β1/SMAD3 mediated αSMA and collagen expression. Consistent with observations in cultured human HSCs, CYGB expression was negligible, but 8-OHdG was abundant, in activated αSMA⁺pSMAD2⁺- and αSMA⁺NOX4⁺-positive hepatic stellate cells from patients with NASH and advanced fibrosis.

CONCLUSIONS

Downregulation of CYGB by the TGF-β1/pSMAD2/SP3-M1 pathway brings about ^•OH-dependent oxidative DNA damage in activated hepatic stellate cells from patients with NASH.

LAY SUMMARY

Cytoglobin (CYGB) is a respiratory protein that acts as a scavenger of reactive oxygen species and protects cells from oxidative DNA damage. Herein, we show that the cytokine TGF-β1 downregulates human CYGB expression. This leads to oxidative DNA damage in activated hepatic stellate cells. Our findings provide new insights into the relationship between CYGB expression and the pathophysiology of fibrosis in patients with non-alcoholic steatohepatitis.

Lessons from the post-genomic era: Globin diversity beyond oxygen binding and transport

Vertebrate hemoglobin (Hb) and myoglobin (Mb) were among the first proteins whose structures and sequences were determined over 50 years ago. In the subsequent pregenomic period, numerous related proteins came to light in plants, invertebrates and bacteria, that shared the myoglobin fold, a signature sequence motif characteristic of a 3-on-3 α-helical sandwich. Concomitantly, eukaryote and bacterial globins with a truncated 2-on-2 α-helical fold were discovered. Genomic information over the last 20 years has dramatically expanded the list of known globins, demonstrating their existence in a limited number of archaeal genomes, a majority of bacterial genomes and an overwhelming majority of eukaryote genomes. In vertebrates, 6 additional globin types were identified, namely neuroglobin (Ngb), cytoglobin (Cygb), globin E (GbE), globin X (GbX), globin Y (GbY) and androglobin (Adgb). Furthermore, functions beyond the familiar oxygen transport and storage have been discovered within the vertebrate globin family, including NO metabolism, peroxidase activity, scavenging of free radicals, and signaling functions. The extension of the knowledge on globin functions suggests that the original roles of bacterial globins must have been enzymatic, involved in defense against NO toxicity, and perhaps also as sensors of O₂, regulating taxis away or towards high O₂ concentrations. In this review, we aimed to discuss the evolution and remarkable functional diversity of vertebrate globins with particular focus on the variety of non-canonical expression sites of mammalian globins and their according impressive variability of atypical functions.

Role of cytoglobin, a novel radical scavenger, in stellate cell activation and hepatic fibrosis

Cytoglobin (Cygb), a stellate cell-specific globin, has recently drawn attention due to its association with liver fibrosis. In the livers of both humans and rodents, Cygb is expressed only in stellate cells and can be utilized as a marker to distinguish stellate cells from hepatic fibroblast-derived myofibroblasts. Loss of Cygb accelerates liver fibrosis and cancer development in mouse models of chronic liver injury including diethylnitrosamine-induced hepatocellular carcinoma, bile duct ligation-induced cholestasis, thioacetamide-induced hepatic fibrosis, and choline-deficient L-amino acid-defined diet-induced non-alcoholic steatohepatitis. This review focuses on the history of research into the role of reactive oxygen species and nitrogen species in liver fibrosis and discusses the current perception of Cygb as a novel radical scavenger with an emphasis on its role in hepatic stellate cell activation and fibrosis.

Emerging perspectives on cytoglobin, beyond NO dioxygenase and peroxidase

Cytoglobin is an evolutionary ancient hemoglobin with poor functional annotation. Rather than constrained to penta coordination, cytoglobin's heme iron may exist either as a penta or hexacoordinated arrangement when exposed to different intracellular environments. Two cysteine residues at the surface of the protein form an intramolecular disulfide bond that regulates iron coordination, ligand binding, and peroxidase activity. Overall, biochemical results do not support a role for cytoglobin as a direct antioxidant enzyme that scavenges hydrogen peroxide because the rate of the reaction of cytoglobin with hydrogen peroxide is several orders of magnitude slower than metal and thiol-based peroxidases. Thus, alternative substrates such as fatty acids have been suggested and regulation of nitric oxide bioavailability through nitric oxide dioxygenase and nitrite reductase activities has received experimental support. Cytoglobin is broadly expressed in connective, muscle, and nervous tissues. Rational for differential cellular distribution is poorly understood but inducibility in response to hypoxia is one of the most established features of cytoglobin expression with regulation through the transcription factor hypoxia-inducible factor (HIF). Phenotypic characterization of cytoglobin deletion in the mouse have indicated broad changes that include a heightened inflammatory response and fibrosis, increase tumor burden, cardiovascular dysfunction, and hallmarks of senescence. Some of these changes might be reversed upon inhibition of nitric oxide synthase. However, subcellular and molecular interactions have been seldom characterized. In addition, specific molecular mechanisms of action are still lacking. We speculate that cytoglobin functionality will extend beyond nitric oxide handling and will have to encompass indirect regulatory antioxidant and redox sensing functions.

Cytoglobin Attenuates Neuroinflammation in Lipopolysaccharide-Activated Primary Preoptic Area Cells via NF-κB Pathway Inhibition

Cytoglobin (Cygb) is a hexacoordinate protein, associated with the transport of oxygen, nitric oxide scavenging, tumor suppression and protection against oxidative stress and inflammation. This protein is expressed in brain areas including the preoptic area (POA) of the anterior hypothalamus, the region responsible for the regulation of body temperature. In this study, we show that Cygb is upregulated in the rat hypothalamus 2.5 h and 5 h after intravenous administration of lipopolysaccharide (LPS). We investigated the effect of treatment with Cygb in POA primary cultures stimulated with LPS for 4 h. The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were measured and the results showed that Cygb reduced the concentrations of both cytokines. We further observed a decrease in immunoreactivity of the inflammatory transcription factor nuclear factor-κB (NF-κB), but not NF-IL6 and STAT3, in the nucleus of Cygb-treated POA cells. These findings suggest that Cygb attenuates the secretion of IL-6 and TNF-α in LPS-stimulated POA primary cultures via inhibition of the NF-κB signaling pathway, indicating that this protein might play an important role in the control of neuroinflammation and fever.

Obeticholic Acid Protects against Gestational Cholestasis-Induced Fetal Intrauterine Growth Restriction in Mice

Gestational cholestasis is a common disease and is associated with adverse pregnancy outcomes. However, there are still no effective treatments. We investigated the effects of obeticholic acid (OCA) on fetal intrauterine growth restriction (IUGR) during 17α-ethynylestradiol- (E2-) induced gestational cholestasis in mice. All pregnant mice except controls were subcutaneously injected with E2 (0.625 mg/kg) daily from gestational day (GD) 13 to GD17. Some pregnant mice were orally administered with OCA (5 mg/kg) daily from GD12 to GD17. As expected, OCA activated placental, maternal, and fetal hepatic FXR signaling. Additionally, exposure with E2 during late pregnancy induced cholestasis, whereas OCA alleviated E2-induced cholestasis. Gestational cholestasis caused reduction of fetal weight and crown-rump length and elevated the incidence of IUGR. OCA decreased the incidence of IUGR during cholestasis. Interestingly, OCA attenuated reduction of blood sinusoid area in placental labyrinth layer and inhibited downregulation of placental sodium-coupled neutral amino acid transporter- (SNAT-) 2 during cholestasis. Additional experiment found that OCA attenuated glutathione depletion and lipid peroxidation in placenta and fetal liver and placental protein nitration during cholestasis. Moreover, OCA inhibited the upregulation of placental NADPH oxidase-4 and antioxidant genes during cholestasis. OCA activated antioxidant Nrf2 signaling during cholestasis. Overall, we demonstrated that OCA treatment protected against gestational cholestasis-induced placental dysfunction and IUGR through suppressing placental oxidative stress and maintaining bile acid homeostasis.

Rosiglitazone ameliorates bile duct ligation-induced liver fibrosis by down-regulating NF-κB-TNF-α signaling pathway in a PPARγ-dependent manner

Liver fibrosis is a major cause of morbidity and mortality worldwide. One of its therapeutic targets is peroxisome proliferator-activated receptor γ (PPARγ), with its ligands including rosiglitazone being tested in pre-clinical and clinical studies. However, the effects of rosiglitazone on bile duct ligation (BDL)-induced liver fibrosis and the involved mechanisms remain unknown. Herein, we used floxed control (PPARγ^fl/fl) and hepatocyte-specific PPARγ deficient (HepPPARγ KO) mice to conduct BDL to induce liver fibrosis and treated the animals with rosiglitazone. After one week of BDL, mice in BDL group displayed liver injury evidenced by increased collagen content, fibrosis area, necrosis area and apoptotic cells, and elevated alkaline phosphatase and alanine transaminase activities in serum. Interestingly, rosiglitazone ameliorated BDL-induced liver injury in PPARγ^fl/fl mice but not in HepPPARγ KO mice. Mechanistically, rosiglitazone reduced BDL-induced collagen content by downregulating fibrotic related genes including transforming growth factor β1, α-smooth muscle actin and collagen type I α1, and decreased inflammation cytokine tumor necrosis factor α level by inhibiting phosphorylation of nuclear factor-κB in a PPARγ-dependent manner. Based on findings above, we demonstrated that rosiglitazone can ameliorate BDL-induced liver fibrosis in mice and confirmed its critical functions on fibrosis by regulating NF-κB-TNF-α pathway in a PPARγ-dependent manner.

Hepatoprotective potential of standardized Ficus species in intrahepatic cholestasis rat model: Involvement of nuclear factor-κB, and Farnesoid X receptor signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Ficus is an important commercial crop not only for its nutritive value but also, for its medicinal value. Several Ficus species have been traditionally used in the Egypt, Indian and Chinese as carminative, astringent, antibacterial, hepatoprotective, and hypolipidemic agents.

AIM OF THE STUDY

To standardize and compare the possible hepatoprotective potential of the ethanolic extract of leaves of five tested Ficus species namely: Ficus mysorensis Roth ex Roem. & Schult, Ficus pyriformis Hook. & Arn., Ficus auriculata Lour., Ficus trigonata L., and Ficus spragueana Mildbr. & Burret in the intrahepatic cholestasis rat model induced by 17α-Ethinylestradiol (EE) and to explore the mechanism of action with respect to their phytochemical constituents.

MATERIALS AND METHODS

Determination of the total phenolic and flavonoid contents, chromatographic examination and acute oral toxicity test were performed on the tested Ficus extracts. Animals were divided into 8 groups. Group 1, served as control for 2 weeks. Group 2, untreated cholestatic rats. Groups 3-8, pretreated with Ficus extracts (100 mg/Kg/day, p.o) or ursodeoxycholic acid (as reference drug) for 2 weeks and injected by EE in the last 5 days. Serum liver function test, 5'-nucleotidase (5'-N), total bile acids (TBA), total cholesterol (T.C) and phospholipids were assayed. Also, hepatic Na⁺/K⁺-ATPase, nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), hepatocyte growth factor (HGF), hemeoxygenase-1 (HO-1), and markers of oxidative stress were investigated. Furthermore, molecular docking study was performed to explore the ability of the major constituents of Ficus to interact with Farnesoid X receptor (FXR).

RESULTS

Four phenolic compounds (gallic, chlorogenic acid, caffeic acids and rutin) were identified. Chlorogenic acid and rutin represented the major constituents of Ficus extracts. Simultaneous administration of Ficus extracts with EE effectively: i- preserved liver function, TBA, T.C and phospholipids, ii- suppressed the pro-inflammatory cytokines (NF-κB and TNF-α), iii- enhanced hepatic regeneration (HGF) and antioxidant defense system. Furthermore, molecular docking reveals that rutin and chlorogenic acid effectively act as FXR agonists.

CONCLUSION

Among the tested extracts, Ficus spragueana Mildbr. & Burret enriched with phenolics exhibited a pronounced hepatoprotective activity and may provide a new therapeutic approach for estrogen-induced cholestasis.

Selective overexpression of cytoglobin in stellate cells attenuates thioacetamide-induced liver fibrosis in mice

Cytoglobin (CYGB), discovered in hepatic stellate cells (HSCs), is known to possess a radical scavenger function, but its pathophysiological roles remain unclear. Here, for the first time, we generated a new transgenic (TG) mouse line in which both Cygb and mCherry reporter gene expression were under the control of the native Cygb gene promoter. We demonstrated that the expression of Cygb-mCherry was related to endogenous Cygb in adult tissues by tracing mCherry fluorescence together with DNA, mRNA, and protein analyses. Administration of a single dose (50 mg/kg) of thioacetamide (TAA) in Cygb-TG mice resulted in lower levels of alanine transaminase and oxidative stress than those in WT mice. After 10 weeks of TAA administration, Cygb-TG livers exhibited reduced neutrophil accumulation, cytokine expression and fibrosis but high levels of quiescent HSCs. Primary HSCs isolated from Cygb-TG mice (HSCCygb-TG) exhibited significantly decreased mRNA levels of α-smooth muscle actin (αSMA), collagen 1α1, and transforming growth factor β-3 after 4 days in culture relative to WT cells. HSCsCygb-TG were resistant to H2O2-induced αSMA expression. Thus, cell-specific overexpression of Cygb attenuates HSC activation and protects mice against TAA-induced liver fibrosis presumably by maintaining HSC quiescence. Cygb is a potential new target for antifibrotic approaches.

Cytoglobin ameliorates the stemness of hepatocellular carcinoma via coupling oxidative-nitrosative stress signals

Cancer stem cells (CSCs) account for tumor self-renewal and heterogeneity. Oxidative-nitrosative stress (ONS) is an independent etiologic factor throughout tumorigenesis. Emerging evidences indicated that the interaction of ONS with CSCs contributes to tumor progression and resistance to chemoradiotherapy. Cytoglobin (Cygb) is a member of human hexacoordinate hemoglobin family and acts as a dynamic mediator of redox homeostasis. We observed that Cygb is significantly deregulated in human hepatocellular carcinoma (HCC) tissue and its decrease aggravates the growth of liver cancer stem cells (LCSCs) and increases the subpopulation of CD133(+) LCSCs. Cygb restoration inhibits HCC proliferation and LCSC growth, and decreases the subpopulation of CD133 (+) LCSCs in vitro. We found that Cygb absence promotes LCSC phenotypes and PI3 K/AKT activation, whereas Cygb restoration inhibits LCSC phenotypes and PI3 K/AKT activation. Furthermore, exogenous antioxidants can eliminate the inhibitory effect of Cygb to LCSC growth and phenotypes, as well as PI3 K/AKT activation. Collectively, this study demonstrated that cytoglobin functions as a tumor suppressor and targets CSCs at an ONS-dependent manner. Thus, Cygb restoration could be a novel and promising therapeutic strategy against HCC with aberrant ROS/RNS accumulation.

Fibroblast growth factor 2 (FGF2) regulates cytoglobin expression and activation of human hepatic stellate cells via JNK signaling

Cytoglobin (CYGB) belongs to the mammalian globin family and is exclusively expressed in hepatic stellate cells (HSCs) in the liver. In addition to its gas-binding ability, CYGB is relevant to hepatic inflammation, fibrosis, and cancer because of its anti-oxidative properties; however, the regulation of CYGB gene expression remains unknown. Here, we sought to identify factors that induce CYGB expression in HSCs and to clarify the molecular mechanism involved. We used the human HSC cell line HHSteC and primary human HSCs isolated from intact human liver tissues. In HHSteC cells, treatment with a culture supplement solution that included fibroblast growth factor 2 (FGF2) increased CYGB expression with concomitant and time-dependent α-smooth muscle actin (αSMA) down-regulation. We found that FGF2 is a key factor in inducing the alteration in both CYGB and αSMA expression in HHSteCs and primary HSCs and that FGF2 triggered the rapid phosphorylation of both c-Jun N-terminal kinase (JNK) and c-JUN. Both the JNK inhibitor PS600125 and transfection of c-JUN-targeting siRNA abrogated FGF2-mediated CYGB induction, and conversely, c-JUN overexpression induced CYGB and reduced αSMA expression. Chromatin immunoprecipitation analyses revealed that upon FGF2 stimulation, phospho-c-JUN bound to its consensus motif (5'-TGA(C/G)TCA), located -218 to -222 bases from the transcription initiation site in the CYGB promoter. Of note, in bile duct-ligated mice, FGF2 administration ameliorated liver fibrosis and significantly reduced HSC activation. In conclusion, FGF2 triggers CYGB gene expression and deactivation of myofibroblastic human HSCs, indicating that FGF2 has therapeutic potential for managing liver fibrosis.

The Hemoglobin Homolog Cytoglobin in Smooth Muscle Inhibits Apoptosis and Regulates Vascular Remodeling

OBJECTIVE

The role of hemoglobin and myoglobin in the cardiovascular system is well established, yet other globins in this context are poorly characterized. Here, we examined the expression and function of cytoglobin (CYGB) during vascular injury.

APPROACH AND RESULTS

We characterized CYGB content in intact vessels and primary vascular smooth muscle (VSM) cells and used 2 different vascular injury models to examine the functional significance of CYGB in vivo. We found that CYGB was strongly expressed in medial arterial VSM and human veins. In vitro and in vivo studies indicated that CYGB was lost after VSM cell dedifferentiation. In the rat balloon angioplasty model, site-targeted delivery of adenovirus encoding shRNA specific for CYGB prevented its reexpression and decreased neointima formation. Similarly, 4 weeks after complete ligation of the left common carotid, Cygb knockout mice displayed little to no evidence of neointimal hyperplasia in contrast to their wild-type littermates. Mechanistic studies in the rat indicated that this was primarily associated with increased medial cell loss, terminal uridine nick-end labeling staining, and caspase-3 activation, all indicative of prolonged apoptosis. In vitro, CYGB could be reexpressed after VSM stimulation with cytokines and hypoxia and loss of CYGB sensitized human and rat aortic VSM cells to apoptosis. This was reversed after antioxidant treatment or NOS2 (nitric oxide synthase 2) inhibition.

CONCLUSIONS

These results indicate that CYGB is expressed in vessels primarily in differentiated medial VSM cells where it regulates neointima formation and inhibits apoptosis after injury.